A number of conventional intake system where a structure for generating an intense tumble flow is provided within an intake pipe (also referred to as intake port) have been proposed. In Patent Document 1, for example, a partition plate (also referred to as partition wall, separation wall or the like) is placed inside the intake pipe in the longitudinal direction so that the intake pipe is divided into a tumble passage and a control passage. In addition, an intake flow control valve which can be opened and closed is placed on the control passage side, and left and right partition walls are provided on the tumble passage side so that the tumble flow can be stratified. In addition, Patent Document 2 discloses an intake system where a partition plate having at least connecting pores in the portion which injected fuel collides with is used. In this intake system, the portion which injected fuel collides with has an uneven surface and connecting pores so that the dispersion, evaporation and atomization of fuel can be accelerated and liquid dropping of the injected fuel can be prevented, and thus, the combustion can be stabilized. Furthermore, Patent Document 3 discloses an intake system where an intake control valve is placed upstream from a partition wall, which divides the inside of an intake port into two passages, and connecting passages in slit form are provided in the partition wall. The above described connecting passages are provided on the upstream end side of the partition wall so that they face a local low pressure region which is created on the downstream side when the intake control valve is closed. In the intake system of Patent Document 3, the second passage on the lower side is closed with the intake control valve when a tumble flow is created, and thus, an intake flow is created in the first passage on the upper side. At this time, an intake flow for taking air from the second passage to the first passage is created in the above described connecting passage so that the tumble flow can be intensified.
Patent Document 1: Japanese Patent Application Publication No. 06-159079
Patent Document 2: Japanese Patent Application Publication No. 05-209582
Patent Document 3: Japanese Patent Application Publication No. 2004-124836